Determining those patients with Cushing's disease who are completely cured following microsurgical resection of pituitary tumors from those who are incompletely cured has traditionally required prolonged post-operative follow-up. Intraoperative changes in serum ACTH and cortisol levels in patients undergoing transphenoidal microsurgery may help delineate sooner those patients in whom surgery was successful from those in whom further intervention is needed.